There a three main components of the imaging system: the high resolution imager,
the medium resolution imager, and the side-looking imager.

Each
of these cameras takes a picture of Titan's surface in a different direction
and at a different
resolution to produce a "triplet" collection of three images
which may be combined with other triplets to create a mosaic of the surface.

the UA mall, from the roof of LPL

The
cameras themselves contain the same technology as in basic digital cameras
here
on earth. When Cassini was launched, however, NASA scientists paid quite
a bit for this "new technology".

The
high resolution imager, as the name implies, takes high resolution pictures.
The lens of this camera is pointed at an
downward (around 90-degree
angle) at the ground. The medium resolution imager takes mid-resolution pictures
at about a 45-degree angle between the surface and the horizontal (or horizon).
Finally, the side-looking imager takes lower resolution pictures with the
lens pointed horizontally away from the probe (0-degree angle).

These cameras don't take pictures like you may
expect. When the images are sent back to earth, there is quite a bit
of overlap between images, as a result of how much the probe rotates during
the descent and the overlap between the field of view of the cameras. DISR
scientists study these images for similarities, such as physical features
common to more than one image, and begin to construct a mosaic like a jigsaw
puzzle.

Before
the instrument was launched, we performed some tests of the imaging system
at the Mount Lemmon fire tower, the UA Mall,
and from a helicopter over the town of Red Rock, just north of Tucson. These
mosaics
give us the best estimate of what the surface of Titan may look like when
we descend...